1. Field of the Invention
The present invention relates to a radiation sensitive resin composition and, more specifically, a radiation sensitive resin composition useful as a resist suitable for microfabrication using ultraviolet rays, far ultraviolet rays, X-rays, or various radioactive rays such as charged particle rays.
2. Description of the Background Art
In the field of microfabrication, typically in the manufacture of elements for integrated circuits, a rapidly progressing trend is to define design rules for the lithographic process with finer dimensions, with the aim of achieving higher degrees of circuit integration. Accordingly, development of a lithographic process that is capable of microfabrication with precision for a line width of 0.5 .mu.m or less has been vigorously pursued in recent years.
However, drawing such a minute pattern as above with a high enough precision is very difficult with the conventional process based on visible rays (wavelength: 700-400 nm) or near ultraviolet rays (400-300 nm). For this reason, lithographic processes based on radiation with a shorter wavelength (300 nm or less) that is capable of achieving a greater focal depth and establishing finer design rules are being proposed.
As the lithographic processes using such short wavelength radiation, for example, methods based on a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), X-rays such as synchrotron radiation, or charged particle radiation such as electron beams are being proposed. In addition, International Business Machines, Inc. ("IBM") has proposed a "chemically amplified resist" as a high-resolution resist suitable for use with these short wavelength radioactive rays. Improvements in the chemically amplified resist are now being actively pursued.
With a chemically amplified resist, acid is generated when radioactive rays irradiate (a process hereinafter termed "exposure") the photoacid generator contained in such a resist. The acid thus generated acts as a catalyst to trigger chemical reactions such as alteration of polarity, cleavage of chemical bonds, or crosslinking within the exposed part of the resist film. The resulting change in solubility characteristics of the exposed part to a developing solution can then be utilized to develop a pattern.
Among the existing chemically amplified resists, those known for relatively good resist performance include resists based on resins in which (1) an alkali affinitive group in the alkali soluble resin is protected by a t-butyl ester group or t-butoxycarbonyl group (see Japanese Patent Publication No. 27660/1990 or EP 102450 A) ; (2) an alkali affinitive group in the alkali soluble resin is protected by a ketal group (see Japanese Patent Application Laid-Open No. 140666/1995); and (3) an alkali affinitive group in the alkali soluble resin is protected by an acetal group (see Japanese Patent Application Laid-Open No. 161436/1990 and Japanese Patent Application Laid-Open No. 249682/1993).
However, it has been pointed out that each of these chemically amplified resists has a peculiar drawback, giving rise to various obstacles for actual application to microfabrication, particularly with a critical design dimension of 0.25 .mu.m or less.
Specifically, various known chemically amplified resists have to be adopted in each narrowly defined use. Although good resolution with satisfactory appearance is generally available for line-and-space patterns or isolated patterns, resolution is often insufficient for contact holes. Further, popularization of multimedia information processing in recent years has necessitated that designs of semiconductor devices become more diversified. This, coupled with a requirement for a cost reduction to cope with the rapid price decrease in the marketplace, has created a strong demand for the development of a chemically amplified resist which is capable of resolving not only the usual line-and-space patterns but also isolated patterns as well as contact hole patterns with satisfactory appearance and therefore is useful in multiple applications.
The present invention has been made in consideration of the above circumstances and as a result of detailed research and examination applied to the constituents of the chemically amplified resists.
Accordingly, an object of the present invention is to provide a radiation sensitive resin composition suitable as a chemically amplified resist that has efficient response to various radioactive rays. Such a resist is capable of resolving any of line-and-space patterns, isolated patterns, and contact hole patterns with satisfactory appearance and resolution, and therefore is applicable to multiple uses.